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Anatomy & Physiology
Ch 9 Senses Worksheet
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What exactly are sensory receptors?
Sensory receptors are structures that are associated with the dendrites of sensory neurons that convert a stimulus into
action potentials. How they do this depends on the receptor.
What is adaptation, in the context of the senses?
Adaptation is a reduction in sensitivity in the presence of a constant stimulus.
Explain the basic difference between general senses and special senses.
General senses have their receptors distributed throughout the body, whereas special senses have their receptors located
in one place, within specialized structures called sense organs.
General Senses
Pain (Nociception)
Location of receptors: Throughout the skin, joints, bones, blood vessels and organs.
Receptors are sensitive to: Extremes of temperature, mechanical damage or chemicals.
Why is the sensation of pain (however unpleasant) a necessary adaption for survival? It tells the
body when something is wrong and alerts the person consciously to damage they might otherwise be unaware of.
Temperature (Thermoreception)
Location of receptors: Throughout the skin, muscles, liver and hypothalamus (brain).
Receptors are sensitive to: Changes in temperature.
What role does adaptation play in thermoreception? Temperature receptors are more active when
temperature is changing, and adapt quickly to constant temperatures. This is why lukewarm water can feel hotter
when your hands are very cold.
Mechanoreception
Touch (Tactile reception)
Location of receptors: Throughout body, especially skin.
Receptors are sensitive to: Displacement, distortion or movement of the receptors.
Why do you think there is a greater density of touch receptors on the hands, lips and
tongue, than there is on the surface of the back? The areas with the densest collections of
receptors can feel objects with better detail. Since we manipulate objects with our hands, and feel the
texture of foods with our lips and tongue, it makes sense to have denser collections of touch receptors
there.
Pressure (Baroreception)
Location of receptors: Organs, blood vessels, respiratory, digestive or urinary tracts.
Receptors are sensitive to: Expansion or recoil of surrounding tissues.
Why do we need baroreceptors in our blood vessels? To maintain adequate blood flow to
tissues, in particular brain, the body must adjust keep adequate pressure to tissues by adjusting the diameter of
blood vessels. The sensation of pressure allows the body to make these adjustments.
Body Position (Proprioreception)
Location of receptors: Ligaments, tendons and muscles around joints.
Receptors are sensitive to: How far they are stretched.
Why might people who undergo rapid growth spurts lose physical coordination and be
temporarily more “clumsy”? Your brain takes information from proprioreceptors to indicate body
position. If the distance to your hands or feet changes quickly due to rapid growth without giving the brain
time to “re-learn”, the brain may respond as if the hands and feet were in their “old” position, causing lack
of coordination.
Chemoreception
Location of receptors: Throughout body, depending on type.
Receptors are sensitive to: Specific molecules, ions or atoms.
What role do chemoreceptors play in maintaining homeostasis? They allow your body to monitor
concentrations of important chemicals, from ions like Na and K, to pH.
Special Senses
Smell (Olfaction)
Location of receptors: Nasal epithelium (lining of the nasal cavity).
Receptors are sensitive to: Chemicals in the air.
Why does smell – more than any other sense – trigger memories and emotions? The pathways
that carry olfactory information pass directly through the area of your brain responsible for laying down memories
(unlike the other special senses).
Taste (Gustation)
Location of receptors: The surface of the tongue.
Receptors are sensitive to: Chemicals dissolved in saliva (usually from food).
Why have we evolved an unpleasant response to tastes such as sour and bitter, and a
pleasant response to sweet, salty, umami and water? Sour and bitter indicate foods that are acidic (or
potentially spoiled) and basic, both of which can be damaging to the body. Foods that are sweet are rich in
carbohydrates and fats, which provide energy. Salty foods provide important minerals, umami foods are rich in
amino acids (often protein), and water is essential for cellular function. In other words, if it is good for survival we
have evolved a pleasant sensation, but if it is dangerous we have evolved a negative reaction.
Vision
Location of receptors: Retina (inner posterior surface of your eyeball).
Receptors are sensitive to: Photons of light.
What are rods and cones, and which type are affected in colorblindness? Rods are sensitive to
different intensities of light, and cones to different wavelengths (or colors) of light). Colorblindness is caused by
abnormal formation of cones.
Hearing (Audition)
Location of receptors: Inner ear.
Receptors are sensitive to: Vibration in the air (sound).
Why is it possible to lose the ability to hear certain frequencies (usually high-frequency) but still
not lose all hearing? Different frequencies have different receptors, and they are damaged by
overstimulation. So it is possible to have partial hearing loss when overexposed to one stimulus – say, really loud
guitars in the case of Pete Townshend of The Who.
Balance (Equilibrium)
Location of receptors: Inner ear.
Receptors are sensitive to: Rotational movement of the head.
Why does spinning around many times make it difficult to then walk in a straight line? Spinning
repeatedly gets the fluid in the semicircular ducts moving, and when your head stops the fluid keeps moving,
giving a disorienting sensation of movement which makes it hard to coordinate appropriate movement.